This project attempts to understand the biochemical basis for T cell interactions with other cells in the immune system. During the past year we have been able to analyze T cell activation by antigen and Ia molecules on antigen-presenting cells in terms of a receptor occupancy model, originally used to describe hormone activation of sensitive target cells. Using this model we were able to design experiments to support the hypothesis that variations in antigen dose response curves as a function of rest after antigen-induced stimulation of T cell clones are related to variations in antigen receptor number or affinity. This variation may play a critical role in the phenomenon of T cell memory.